The present invention relates to a pen pressure device for bringing a pen into contact with or separation from a paper in an X-Y plotter and the like.
In the X-Y plotter, the pen is arranged such that a front end thereof is opposed to the paper, and is moved in two directions of an X-axis and a Y-axis which are perpendicular to each other. Alternatively, the pen is moved in either direction of the X-axis or the Y-axis, and the paper is moved in the other direction. Then, the pen is brought into contact with or separation from the paper by the pen pressure device, thereby printing a graphic or the like on the paper moving in the two directions relative to the pen.
Conventionally, the above-mentioned X-Y plotter has employed a pen pressure device 1 as shown in FIGS. 4 and 5.
Referring to FIGS. 4 and 5, a carriage 4 of the X-Y plotter is movable in a direction parallel to a paper plane of a paper 3 along a pair of guide rods 2. The carriage 4 is provided at its upper surface with a mount portion 6 on which a pen 5 is axially movably mounted in a manner that a front end of the pen 5 is opposed to the paper 3. The pen 5 is formed at its front side with a small-diameter portion 8 through a frusto-conical tapered portion 7. The small-diameter portion 8 is inserted through a guide hole 9 formed through the carriage 4, and is adapted to contact under pressure with the paper 3.
A coiled pen pressure spring 10 is mounted at a rear end of the mount portion 6 of the carriage 6 in such a manner as to contact under pressure with a rear end of the pen 5. The pen pressure spring 10 acts to bias the pen 5 toward the paper 3 under a predetermined pressure suitable for writing on the paper 3. A lever 11 is rockably supported at its lower end by a pin 12 to the carriage 4. The lever 11 is formed at its upper end portion with a circular hole 13 with which the small-diameter portion 7 of the pen 5 is engaged. A coiled return spring 14 is located around the small-diameter portion 8 of the pen 5 to bias the circular hole 13 clockwise as viewed in FIG. 4 and urge the pen 5 away from the paper 3. A spring force of the return spring 14 is set stronger than that of the pen pressure spring 10. Accordingly, when both the spring forces of the springs 10 and 14 are applied to the pen 5 at the same time in counter directions, the pen 5 is separated from the paper 3 as shown in FIG. 4, which is called a pen-up condition.
In the carriage 4 is accommodated a solenoid 15 having a plunger 16 for biasing the lever 11 counterclockwise against the spring force of the return spring 14. When the solenoid 15 is excited, the plunger 16 urges the lever 11 to rotate the same counterclockwise from the position shown in FIG. 4, thus eliminating the influence of the spring force of the return spring 14 to the pen 5 through the lever 11. Accordingly, the pen 5 is brought into pressure contact with the paper 3 by the operation of the pen pressure spring 10 as shown in FIG. 5, which is called a pen-down condition.
With this arrangement, the pen 5 is moved to select the pen-up condition of FIG. 4 or the pen-down condition of FIG. 5 while the carriage 4 is moved, and the solenoid 15 is excited or deexcited according to information of drawing, thus forming a desired drawing on the paper 3.
However, in the conventional pen pressure device as mentioned above, the spring force of the return spring 14 must be set much greater than that of the pen pressure spring 10, so as to stably retain the pen 5 under the pen-up condition shown in FIG. 4. In selecting the pen-down condition, a large output of the solenoid 15 urging the lever 11 is necessary for eliminating the influence of the spring force of the return spring 14. As a result, the solenoid 15 must be made large-scale to cause an increase in costs, power consumption of the solenoid 15 and a running cost. Further, a high noise is generated upon rotation of the lever 11.
In the case that the pen-down condition shown in FIG. 5 is maintained for a relatively long time, such as a case of drawing a line on the paper 3 by the pen, the solenoid 15 must continue to be supplied with current or it must be of a self-holding type. When the self-holding type solenoid 15 is used, it is required to usually provide a spring as an operational load of the solenoid 15, and therefore, a further greater output of the solenoid 15 is necessary. Furthermore, when the current is continuously supplied to the solenoid 15 during the pen-down condition, a power consumption is more increased.